Neoplasia affects the urinary tract uncommonly in dogs and rarely in cats. Clinical signs depend on the part(s) of the urinary system affected and can include lethargy, hematuria, weight loss, and stranguria. Treatment depends on the tumor type and location and can include chemotherapy, surgery, radiation, or a combination of these.
Renal Neoplasia in Dogs and Cats
Neoplasia that affects the kidney is uncommon but does occur. Various tumor types can affect the kidney; dogs are most commonly affected by epithelial tumors, whereas sarcomas and nephroblastomas are rarely reported.
Primary malignant renal neoplasia (except nephroblastomas) is most common in middle-aged to older animals.
No breed predilection for renal neoplasia has been reported, except for heritable predilection for the development of bilateral, multifocal cystadenocarcinomas in German Shepherd Dogs, generally between 5 and 11 years old.
The most common primary malignant renal neoplasia is renal carcinoma, which originates from the renal tubular epithelium. Usually, it is unilateral, located at one pole of the kidney, and well demarcated. Size varies from microscopic to several times that of the normal kidney.
Renal carcinomas metastasize early to various organs—most commonly the contralateral kidney, lungs, liver, and adrenal glands.
Nephroblastomas arise from vestigial embryonic tissue. They are usually unilateral but occasionally bilateral.
Nephroblastomas occur in young animals and, in dogs, are most commonly diagnosed at < 1 year of age.
No breed predilection for nephroblastoma has been reported. Males are affected twice as commonly as females.
Nephroblastomas can metastasize to regional lymph nodes, liver, and lungs.
Transitional cell carcinomas (TCCs), also called urothelial carcinomas, arise from transitional epithelium of the renal pelvis, ureter, bladder, or urethra (see Neoplasia of the Lower Urinary Tract).
Other types of primary malignant renal neoplasia are uncommon and include hemangiosarcomas, fibrosarcomas, leiomyosarcomas, and squamous cell carcinomas.
The kidneys are a common site of metastatic or multicentric neoplasia. Metastatic lesions can be unilateral or bilateral. Lymphoma is the most common multicentric tumor involving the kidneys.
With the exception of renal lymphoma, renal neoplasia is rare in cats.
Clinical Findings of Renal Neoplasia
Clinical signs of renal neoplasia are nonspecific and include weight loss, anorexia, depression, and fever. Bilateral renal neoplasia uncommonly destroys sufficient renal tissue to cause chronic kidney disease (CKD) and associated signs of uremia. Observant owners might notice “lumps” in their animal’s abdomen or abdominal enlargement. Persistent hematuria, usually microscopic, can occur.
Rarely, renal tumors produce excessive amounts of erythropoietin, resulting in erythrocytosis.
Diagnosis of Renal Neoplasia
Diagnostic imaging
Cytological examination and/or biopsy
History and clinical signs can indicate a mass in the area of the kidneys, or renomegaly, which can be confirmed by radiography, ultrasonography, or CT. Radiographs of the thorax can reveal metastatic disease.
Neoplastic cells occasionally can be found in urine sediment. A tissue sample suitable for diagnosis can be obtained via catheterization. Cystoscopic biopsy can be an effective method to obtain a diagnostic sample in dogs with TCC of the bladder and urethra, especially in females.
Percutaneous needle aspiration and cytological examination can be sufficient to diagnose renal lymphoma in cats and dogs, particularly when there is diffuse involvement or, with ultrasonographic guidance, when there is multifocal disease.
Histological examination of tissue obtained by cystoscopy, needle biopsy, or surgical wedge biopsy is often necessary to determine the type of tumor.
Treatment of Renal Neoplasia
Surgery
Chemotherapy
Treatment of renal tumors (except lymphoma) usually involves surgical removal; unilateral nephrectomy is usually required. Lymphoma is best managed by combination chemotherapy. Chemotherapy is generally ineffective against renal tumors other than lymphoma.
Neoplasia of the Lower Urinary Tract in Dogs and Cats
Neoplasia of the ureters, bladder, and urethra is uncommon in dogs and rare in cats.
In the lower urinary tract, primary neoplasia is more likely to be malignant than benign. Papillomas, leiomyomas, fibromas, neurofibromas, hemangiomas, rhabdomyomas, and myxomas occur infrequently.
Among the types of primary malignant neoplasia of the lower urinary tract, TCCs are the most frequently diagnosed in both dogs and cats. Squamous cell carcinomas, adenocarcinomas, fibrosarcomas, leiomyosarcomas, rhabdomyosarcomas, hemangiosarcomas, and osteosarcomas also are found.
TCCs (see bladder radiograph and pneumocystogram) can be solitary or multiple papillary-like projections from the mucosa or can develop as a diffuse infiltration of the ureter, bladder, prostate, and/or urethra. Cystic TCCs are more common in certain breeds of dogs (particularly Scottish Terriers), have been associated with prior cyclophosphamide therapy, and can be linked to exposure to herbicides and older-generation insecticides.
Courtesy of Ontario Veterinary College.
TCCs are highly invasive and metastasize frequently, most commonly to regional lymph nodes and lungs. Ureteral and bladder neoplasia can cause chronic obstruction to urine flow with secondary hydronephrosis. Urethral tumors are more likely to cause acute obstructive uropathy.
Intractable secondary bacterial urinary tract infections are commonly associated with neoplasia of the bladder and urethra.
Clinical Findings of Lower Urinary Tract Neoplasia
Hematuria, dysuria, stranguria, and pollakiuria are the most common clinical signs of lower urinary tract neoplasia. Animals with ureteral obstruction and unilateral hydronephrosis can show signs of abdominal pain and have a palpably enlarged kidney. Signs of uremia can be apparent in animals with bilateral ureteral obstruction and hydronephrosis or with urethral obstruction. The bladder wall may be thickened, and a cordlike urethra or urethral mass(es) may be palpable rectally.
Diagnosis of Lower Urinary Tract Neoplasia
Urinalysis
Advanced imaging of the urinary tract
BRAF genetic testing
Biopsy
Lower urinary tract signs are common with lower urinary tract neoplasia; however, they must be differentiated from other causes of lower urinary tract disease. History and clinical signs are highly suggestive of lower urinary tract disease in animals with tumors of the bladder or urethra.
Appropriate workup includes urinalysis and advanced imaging of the urinary tract. Urinalysis frequently reveals hematuria, and secondary infection can be evident. Chronic, uncomplicated urinary tract infections must be differentiated from those associated with neoplasia. Neoplastic cells can be found in the sediment, particularly with TCCs (see histological image).
Courtesy of Ontario Veterinary College.
Detection of cells containing the BRAF mutation in urine samples of dogs with suspected TCC/urothelial carcinoma is a sensitive and specific noninvasive test for the most common type of bladder cancer. Urine testing is now routinely used to detect this BRAF mutation in dogs with urinary tract masses or suspicious clinical signs. Because of its high specificity, a positive BRAF genetic test result is diagnostic for TCC/urothelial carcinoma.
Cystourethrography, retrograde urethrography, or ultrasonography is generally necessary to determine the location and extent of the tumor.
Biopsy of the tumor is required for definitive diagnosis if BRAF genetic test results are negative.
Treatment of Lower Urinary Tract Neoplasia
Chemotherapy
COX inhibitors
Management of complications
TCCs are frequently located at the trigone of the bladder or in the urethra, making complete surgical excision unlikely in most cases.
Medical management is the foundation of treatment in most cases of lower urinary tract neoplasia and typically involves a combination of chemotherapy and COX inhibitors (eg, piroxicam [0.3 mg/kg, PO, every 24 hours]; deracoxib [3 mg/kg, PO, every 24 hours]; firocoxib [5 mg/kg, PO, every 24 hours]—all administered indefinitely, as tolerated). Radiotherapy can be used in some cases. Treatment is not usually curative; however, dogs often live a year or more with a good quality of life after diagnosis.
Complications such as urinary tract infections and ureteral or urethral obstruction are possible and must be identified and managed.
Key Points
Tumors of the kidneys are uncommon in dogs and rare in cats. With the exception of renal lymphoma, treatment is typically surgical.
The most common tumor of the urinary bladder in dogs is transitional cell carcinoma (TCC)/urothelial carcinoma, which often presents with lower urinary tract signs that must be differentiated from other causes of lower urinary tract disease.
Treatment for TCC is usually medical (a combination of chemotherapy and COX inhibitors).
For More Information
Fulkerson CM, Knapp DW. Tumors of the urinary system. In Vail DM, Thamm DH, Liptak JM. Withrow and MacEwen's Small Animal Clinical Oncology. 6th ed. Elsevier; 2020:645-656.
Breen Lab, North Carolina State University, Canine TCC/UC - Bladder and Prostate Cancer
Also see pet owner content regarding noninfectious diseases of the urinary system in dogs and cats.
